Tris-(3-hydroxyalkyl) phosphine oxide flame retardant compositions

ABSTRACT

Glass filled thermoplastic polyamide polymers such as nylon 6/6 are rendered fire retardant by the addition of an effective amount of a tris-(3-hydroxyalkyl) phosphine oxide such as tris-(3-methyl-3-hydroxypropyl) phosphine oxide.

The present invention relates to glass filled thermoplastic polyamidepolymers which are rendered flame retardant by having combined therewithan effective amount of a tris-(3-hydroxyalkyl) phosphine oxide.

The polyamide nylon 6/6 was one of the first engineering thermoplastics,so called because of its highly rated mechanical, thermal, andelectrical properties to which standard metal design methodology couldbe applied to yield parts having predictable short and long-termperformance characteristics. Since 1955 other polyamides, i.e., nylon 6,6/6, 6/10, 6/12, 6/9, 11, 12 and copolymers like 6/66 have beenintroduced. However, nylon 6/6 and 6 have always dominated the polyamidemarket and account for the majority of nylons used as engineeringthermoplastics.

With the current and future federal requirements obligating automotivemanufacturers to improve the efficiency of their product and reduce fuelconsumption, there is a substantial growth in the use of engineeringplastics as a replacement for metal to achieve weight reduction. At thepresent time, nylon is the dominant engineering thermoplastic fortransportation end uses.

Polyamides such as thermoplastic nylons, are in general, characterizedas being relatively stable thermally upon long exposure to processingtemperatures and shear. Upon exposure to flame, however, they burn quitereadily. The flammability is characterized by dripping behavior of theburning nylons. There is a substantial and increasing demand for flameretardant nylon.

To meet flame retardant requirements, nylon is customarily compoundedwith flame retardant additives, i.e., organic halogen compounds plusantimony oxide; the most often used combination being 17-20% of apolychloro bicyclic hydrocarbon plus 5% antimony trioxide. Sometimesiron oxide is used with the organohalogen compound. Red phosphorus hasalso been used as a flame retardant for nylon. Such additives, however,frequently degrade or cause degradation under processing conditions(extrusion at about 250° C.) resulting in poor mechanical performance ofthe thermoplastic nylons themselves.

The known flame retardants for nylon such as haloalkyl phosphates,suffer generally from one or more deficiencies including lowcompatibility, low thermal stability or poor fire retardant behavior inmolded nylon components. Additionally, a serious problem posed byorganohalogen flame retardants in nylon is attributable to acidformation, either due to or arising from light exposure or thermaldegradation with the released acid then attacking metal components inend-use applications. Some organohalogen compounds are contraindicatedas fire retardant additives due to toxicity problems of the compound,i.e., mutagenicity.

The present invention is predicated upon the discovery that the additionof a small but effective amount of a tris-(3-hydroxyalkyl) phosphineoxide having the formula: ##STR1## wherein R₁ and R₃ are any radicalselected from the group consisting of hydrogen phenyl and alkyl radicalsof 1 to 4 carbon atoms and R₂ is any radical selected from the groupconsisting of hydrogen phenyl and alkyl radicals of 2 to 4 carbon atoms,provided that when R₁ and R₃ are hydrogen radicals, R₂ is either analkyl radical of 2 to 4 carbon atoms or a phenyl radical, to a glassfilled thermoplastic polyamide substantially improves the flameretardant properties of the polyamide. The addition of atris-(3-hydroxyalkyl) phosphine oxide to the polyamide in the amountrequired to improve flame retardant properties does not adversely modifythe physical properties of the polyamide to a point where its commercialuse is impaired. The tris-(3-hydroxyalkyl) phosphine oxides describedabove are readily compatible with the polyamide and effective when addedin small quantities, i.e., 10-25 parts per hundred. Particularlypreferred compositions are flame retardant nylon molding resins to whichhave been added from about 14 to about 21 parts per hundred of atris-(3-hydroxyalkyl) phosphine oxide.

The flame resistant polyamide-tris-(3-hydroxyalkyl) phosphine oxideblends of the present invention are particularly advantageous for use inthe internal circuitry of appliances, business machines, terminalstrips, connectors and blocks.

The tris-(3-hydroxyalkyl) phosphine oxides of the present invention aremore soluble in water than in polar organic solvents such as chloroform.Such tris-(3-hydroxyalkyl) phosphine oxides combine high compatibilityin polyamides with high thermal stability and excellent fire retardantefficiency either alone or in combination with organohalogen products.

The addition of a tris-(3-hydroxyalkyl) phosphine oxide to glass filledpolyamide such as the various polyamides referred to above, improvesmixing parameters and reduces polymer degradation by lowering theprocessing temperature of the polyamide. Although the present inventionis not to be limited by any theoretical assumption, it is believed thatone possible mechanism by which tris-(3-hydroxyalkyl) phosphine oxideimparts flame resistance is by reaction of the hydroxyl groups uponpyrolysis with the amide linkages in the polymer chain to yield a verytough crosslinked foamed and thermally insulating char, which surpressesfurther resin pyrolysis at the flame front and also eliminates thedripping behavior of the polymer under combustion conditions. The meritsthat may be attributed to such tris-(3-hydroxyalkyl) phosphine oxideflame retardant (relative to conventional flame retardant agents inpresent use) include no corrosion, high ultraviolet stability,nontoxicity and minimal adverse change in the physical properties of thepolymer.

In addition to providing fire resistance to molded glass filledpolyamide parts, the tris-(3-hydroxyalkyl) phosphine oxides may also bepresent in nylon fibers making them flame retardant, more resistant todirt and static build up and rendering the fibers less hydrophobic,thereby improving the wearability. Flame retardant treatments forconventional nylon fabrics are seldom used in practice suggesting thelack of effective treatments for nylon fabrics. The addition oftris-(3-hydroxyalkyl) phosphine oxides to nylon to be used in themanufacture of floor covers is particularly advantageous.

Tris-(3-hydroxyalkyl) phosphine oxide may be prepared by first reactinga 3-hydroxy-1,2-unsaturated olefin such as 1-butene-3-ol or2-butene-3-ol with phosphine in the presence of a free radical catalystas described in U.S. Pat. No. 3,489,811. We have discovered that the useof stoichiometric quantities of reactants (or as little as 4% excessalcohol) reduce the formation of higher molecular weight by-products.The tris-(3-hydroxyalkyl) phosphine obtained by this process is readilyconverted to the corresponding phosphine oxide by oxidation withhydrogen peroxide.

Phosphine oxides having different 3-hydroxyalkyl groups on thephosphorus atom such as: ##STR2## wherein R₁ and R₃ are any radicalselected from the group consisting of hydrogen phenyl and alkyl radicalsof 1 to 4 carbon atoms and R₂ is any radical selected from the groupconsisting of hydrogen phenyl and alkyl radicals of 2 to 4 carbon atoms,provided that when R₁ and R₃ are hydrogen radicals, R₂ is either analkyl radical of 2 to 4 carbon atoms or a phenyl radical, and n iseither 1 or 2, may be prepared by reacting phosphine with a mixture ofallyl alcohol and an alcohol having the formula: ##STR3## wherein R₁,and R₃ are any radical selected from the group consisting of hydrogenphenyl and alkyl radicals of 1 to 4 carbon atoms and R₂ is any radicalselected from the group consisting of hydrogen phenyl and alkyl radicalsof 2 to 4 carbon atoms, provided that when R₁ and R₃ are hydrogenradicals, R₂ is either an alkyl radical of 2 to 4 carbon atoms or aphenyl radical, and oxidizing the resulting product. These mixedphosphine oxides as well as physical mixtures of such mixed phosphineoxides with tris-hydroxyalkyl phosphine oxides such astris-(3-hydroxypropyl) phosphine oxide and/ortris-(3-hydroxy-2-methylpropyl) phosphine oxide are useful additiveshaving application in the present invention.

As indicated above, the less common hydroxy-olefins may be reacted withphosphine to form a 3-hydroxyalkyl phosphine that may be oxidized to thecorresponding phosphine oxide. Examples are 2-butene-1-ol,1-butene-3-ol, 2-heptene-1-ol, cinnamyl alcohol, 2-butyl 2-propene-1-olbutene-2-diol-(1,4) and 2-hydroxymethylpropene-1-ol-3. The resultingproducts, are more costly to manufacture and have the disadvantage ofcontaining less phosphorus than the preferred additives of the presentinvention.

The following examples will more fully illustrate the invention.

EXAMPLE 1 Preparation of Tris-(3-Methyl-3-Hydroxypropyl) Phosphine Oxide

Tris-(3-methyl-3-hydroxypropyl) phosphine may be prepared by the methoddescribed in Example 1 of U.S. Pat. No. 3,489,811.

Into a one liter pressure reactor is placed 381.6 g (5.3 moles)1-butene-3-ol and 20 ml of a solution containing 3 gazobisisobutyronitrile dissolved in 100 ml of 1-butene-3-ol. Thepressure reactor is closed and charged with 36 g (1.06 moles) ofphosphine. The reaction mixture is agitated by rocking the reactor fortwo hours at 80° C. The reaction mixture is permitted to cool to roomtemperature and the pressure vessel is vented in a hood to release anyunreacted phosphine. An additional 20 ml of the azobisisobutyronitrilesolution described above is added to the reactor which is closed and thesystem is again heated to 80° C. and rocked for one hour. The additionof 20 ml of the azobisisobutyronitrile solution is repeated withintermediate agitation at 80° C. for one hour under pressure until allof the azobisisobutyronitrile solution (100 ml) has been added. Thecontents of the reactor are then heated to 80° C. under pressure androcked for an additional five hours.

The solution that results from the above reaction may be vacuumdistilled by heating to about 85° C./1 mm Hg and maintaining at thattemperature and pressure for about four hours to remove volatiles.

The non-volatile residue may be dissolved in an equal volume of a 50:50mixture of isopropanol/methanol and oxidized by stirring with thedropwise addition of a 30% aqueous hydrogen peroxide solution dilutedwith an equal volume of isopropanol. When the exothermic reactionsubsides, the solution of phosphine oxide is tested by adding one dropof the solution to 1 ml of carbon disulfide until no red coloration canbe detected visually in the carbon disulfide layer. This indicatescomplete oxidation of the phosphine to the phosphine oxide.

Following oxidation with hydrogen peroxide, the solvents (water,isopropanol and methanol) are removed from the reaction product byheating to 65° C. under vacuum. The product which remains,tris-(3-methyl-3-hydroxypropyl) phosphine oxide is a useful fireretardant additive for glass filled polyamide resins.

EXAMPLE 2 Preparation of Tris-(1-methyl-3-Hydroxypropyl) Phosphine Oxide

Example 1 above may be repeated using a stoichiometric amount of2-butene-1-ol (crotyl alcohol). Four hundred and fifty grams (13.23moles) phosphine may be reacted with 2,858 g (39.69 moles) of2-butene-1-ol in the presence of 30 g azobisisobutyronitrile over aperiod of nine hours. The temperature varies over a range of 25° C.-170°C. and the pressure over a range of 600 psig to 60 psig. Heating thereaction product to 170° C. at 10 mm Hg pressure will remove volatilesand the residue may be oxidized with hydrogen peroxide (11.90 moles)over two hours at a temperature up to 104° C. The solvents may beremoved by heating to 65° C. under vacuum. The residue is a useful fireretardant for glass filled polyamide resins.

EXAMPLE 3 Preparation of 3-Hydroxypropyl bis-(1-methyl-3-hydroxypropyl)Phosphine Oxide

3-Hydroxypropyl bis-(1-methyl-3-hydroxypropyl) phosphine may be preparedby the method described in Example 1 above.

Into a four liter pressure reactor equipped with a stirrer andthermometer is placed 162.4 g (2.8 moles) of allyl alcohol, 403.2 g (5.6moles) 2-butene-1-ol and 40 ml of a solution containing 9 gazobisisobutyronitrile dissolved in 900 ml of toluene. The pressurereactor is closed and charged with 96 g (2.8 moles) of phosphine. Thereaction mixture is heated with stirring to 60° C. at which temperaturethe reaction becomes exothermic and the temperature rises. Stirring iscontinued and the temperature is maintained at 90° C. with heating andstirring for one hour at which time 50 ml of the azobisisobutyronitrilesolution in toluene is pumped into the reactor. The reaction mixture ismaintained at 90° C. for one hour with stirring after the secondaddition of catalyst. The addition of 50 ml of theazobisisobutyronitrile solution is repeated with continuous stirring at90° C. each hour until all of the azobisisobutyronitrile solution (200moles) has been added. The contents of the reactor are then stirredwhile maintaining the temperature at 90° C. for an additional four hoursafter the pressure in the reaction vessel has dropped to 0 psig.

The reaction mixture may be cooled to room temperature, removed from thereaction vessel and heated up to 35° C. at 2 mm Hg to distill off thevolatile components.

The non-volatile residue may be dissolved in an equal volume ofisopropanol and chilled on ice. The phosphine present in solution isoxidized by the dropwise addition with stirring of a 30% aqueoushydrogen peroxide solution diluted with an equal volume of isopropanol.Inasmuch as the oxidation reaction is exothermic, the course of thereaction may be followed by the temperature increase upon addition ofhydrogen peroxide. When the exotherm subsides, a small aliquot of thereaction mixture is tested after each addition of hydrogen peroxide withhydrogen peroxide test paper and by addition of few drops of thereaction mixture to 1 cc of carbon disulfide. At the end of theoxidation reaction, the observed red color of the carbon disulfideindicative of unoxidized phosphine, disappears and the hydrogen peroxidetest paper indicates the presence of hydrogen peroxide.

When the oxidation of the phosphine to phosphine oxide has beencompleted, the water and isopropanol are removed from the phosphineoxide by heating to 65° C. at 2 mm Hg until all volatiles have distilledoff. The residue is a useful fire retardant additive for nylon resins.

In a similar manner, 1-methyl-3-hydroxypropyl bis-(3-hydroxypropyl)phosphine oxide may be prepared by reacting 2 moles of allyl alcohol and1 mole of 2-butene-1-ol with 1 mole of phosphine and oxidizing thereaction product.

EXAMPLE 4 Effect of Tris-(3-Hydroxyalkyl) Phosphine Oxides As A FlameRetardant For Polyamide Resins

Each of the phosphine oxides described above in Examples 1, 2 and 3 areadded to individual samples of a nylon resin in amounts of 15-20 partsper hundred parts of resin (PHR) and dispersed throughout the resin.Mixing of the additive and resin may be accomplished in a Brabender typemixer (HAAKE RHEOMIX MODEL 600 with REOCORD EU10 attachment,manufactured by Haake Inc., 244 Saddle River Road, Saddle Brook, N.J.07662). The mixing can take place at 265° C. at which temperature someof the additive is volatilized.

In testing the polyamide polymer compositions containing a flameretardant additive, the flame retardant properties are determinedfollowing procedures established by the Underwriter LaboratoriesBulletin No. 94, Standard for Tests for Flammability of PlasticMaterials for Parts in Devices and Appliances; Second Edition, SecondImpression (as revised to Feb. 1, 1974) dated July 30, 1976. TheVertical Burning Test for classifying Materials 94 V-0, 94 V-1 or 94 V-2and described in Section 3 of this publication is used. The phosphineoxides described in Examples 1, 2 and 3 when added to glass filledpolyamide resins in amounts of 15 to 20 part per hundred provideproducts that are classified V0 or V1 by the Vertical Burn Testdescribed above.

The invention in its broader aspects is not limited to the specificdetails shown and described but departure may be made from such detailswithin the scope of the accompanying claims without departing from theprinciples of the invention and without sacrificing its chief advantage.

We claim:
 1. A glass filled thermoplastic polyamide polymer renderedflame retardant by having combined therewith an effective amount of atris-(3-hydroxyalkyl) phosphine oxide having the formula: ##STR4##wherein R₁ and R₃ are any radical selected from the group consisting ofhydrogen, phenyl and alkyl radicals of 1 to 4 carbon atoms and R₂ is anyradical selected from the group consisting of hydrogen, phenyl and alkylradicals of 2 to 4 carbon atoms, provided that when R₁ and R₃ arehydrogen radicals, R₂ is either an alkyl radical of 2 to 4 carbon atomsor a phenyl radical.
 2. The flame retardant polymer of claim 1 whereinthe phosphine oxide is tris-(1-methyl-3-hydroxypropyl) phosphine oxide.3. The flame retardant polymer of claim 1 wherein the phosphine oxide istris-(1-phenyl-3-hydroxypropyl) phosphine oxide.
 4. The flame retardantpolymer of claim 1 wherein the phosphine oxide has the formula: ##STR5##wherein R₁ and R₃ are any radical selected from the group consisting ofhydrogen, phenyl and alkyl radicals of 1 to 4 carbon atoms and R₂ is anyradical selected from the group consisting of hydrogen, phenyl and alkylradicals of 2 to 4 carbon atoms, provided that when R₁ and R₃ arehydrogen radicals, R₂ is either an alkyl radical of 2 to 4 carbon atomsor a phenyl radical and n may be 1 or
 2. 5. The flame retardant polymerof claim 4 wherein the phosphine oxide is 3-hydroxypropylbis-(1-methyl-3-hydroxypropyl) phosphine oxide.
 6. The flame retardantpolymer of claim 4 wherein the phosphine oxide is1-methyl-3-hydroxypropyl bis(3-hydroxpropyl) phosphine oxide.
 7. Theflame retardant polymer of claim 4 wherein the phosphine oxide is amixture of 3-hydroxypropyl bis-(1-methyl-3-hydroxypropyl) phosphineoxide and bis(3-hydroxypropyl) 1-methyl-3-hydroxypropyl phosphine oxide.8. The flame retardant polymer of claim 1 wherein said thermoplasticpolyamide is nylon
 66. 9. The flame retardant polymer of claim 1 whereinsaid thermoplastic polyamide is nylon
 6. 10. The flame retardant polymerof claim 1 to which has been added about 10-25 parts per hundred oftris-(1-methyl-3-hydroxypropyl) phosphine oxide.
 11. The flame retardantpolymer of claim 1 to which has been added about 14-21 parts per hundredof tris-(1-methyl-3-hydroxypropyl) phosphine oxide.
 12. A method ofmanufacturing a flame retardant glass filled polyamide polymer whichcomprises adding thereto an effective amount of a tris-(3-hydroxyalkyl)phosphine oxide having the formula: ##STR6## wherein R₁ and R₃ are anyradical selected from the group consisting of hydrogen, phenyl and alkylradicals of 1 to 4 carbon atoms and R₂ is any radical selected from thegroup consisting of hydrogen, phenyl and alkyl radicals of 2 to 4 carbonatoms, provided that when R₁ and R₃ are hydrogen radicals, R₂ is eitheran alkyl radical of 2 to 4 carbon atoms or a phenyl radical anddistributing the phosphine oxide throughout said polyamide polymer. 13.The method of claim 12 wherein the phosphine oxide istris-(1-methyl-3-hydroxypropyl) phosphine oxide.
 14. The method of claim12 wherein the phosphine oxide is tris-(1-phenyl-3-hydroxypropyl)phosphine oxide.
 15. The method of claim 12 wherein the phosphine oxidehas the formula: ##STR7## wherein R₁ and R₃ are any radical selectedfrom the group consisting of phenyl and alkyl radicals of 1 to 4 carbonatoms and R₂ is any radical selected from the group consisting of phenyland alkyl radicals of 2 to 4 carbon atoms, provided that when R₁ and R₃are hydrogen radicals, R₂ is either an alkyl radical of 2 to 4 carbonatoms or a phenyl radical and n may be 1 or
 2. 16. The method of claim15 wherein the phosphine oxide is 3-hydroxypropylbis-(1-methyl-3-hydroxypropyl) phosphie oxide.
 17. The methd of claim 15wherein the phosphine oxide is 1-methyl-3-hydroxypropylbis-(3-hydroxypropyl) phosphine oxide.
 18. The method of claim 15wherein the phosphine oxide is a mixture of 3-hydroxypropylbis-(1-methyl-3-hydroxypropyl) phosphine oxide and bis-(3-hydroxypropyl)1-methyl-3-hydroxypropyl phosphine oxide.
 19. The method of claim 12wherein said polyamide polymer is nylon
 66. 20. The method of claim 12wherein said polyamide polymer is nylon
 6. 21. The method of claim 12wherein about 14 to 21 parts per hundred oftris-(1-methyl-3-hydroxyalkyl) phosphine oxide are added to thepolyamide polymer.
 22. The method of claim 12 wherein about 5 to 25parts per hundred of tris-(1-methyl-3-hydroxypropyl) phosphine oxide areadded to the polyamide polymer.